Helmets worn by snowmobilers typically include a transparent face shield. This is also often true for motorcycle helmets. The transparent face shield is normally hinge-mounted to the helmet so that the face shield can rotate between a position in front of the user's face to a position above the user's face. Under normal operating conditions, the helmet wearer places the face shield in a closed position to protect the face from wind and/or debris. Usually, the hinge includes a ratchet mechanism to lock the face shield at various degrees of rotation and prevent rotation of the face shield unless the user uses their hand to move the face shield.
Face shields in snowmobile and motorcycle helmets are either clear or tinted. Many snowmobilers and motorcycle riders prefer clear face shields because a tinted face shield is not desirable when it is dark or otherwise not sunny outside. A common occurrence, especially among snowmobilers, is to alternate the use of clear and tinted face shields depending on the weather conditions. The replacement of face shields, however, requires tools and is cumbersome. Also, it is often difficult to store an additional face shield on the vehicle. For these reasons, many snowmobilers or motorcycle riders use helmets having clear, non-tinted face shields, and wear sunglasses underneath the helmet when it is sunny outside. Sunglasses worn underneath a snowmobile helmet tend to fog. Also, the added pressure against the head from the helmet pushing on the ear piece of the sunglasses can cause headaches in some of people.
In addition, it is difficult for a driver to see through a tinted face shield when the vehicle passes from a sunlit area temporarily into a shaded area. This is a common occurrence when snowmobiling because in as much as many snowmobile trails frequently pass into and out of wooded areas. Likewise, when a snowmobiler wearing sunglasses under the helmet drives into a shaded area, such as into the woods, it is difficult to see through the sunglasses due to the relative darkness.